With the fast development of the computer technology, a touch panel is widely used in electronic devices such as a mobile phone, a personal digital assistant (PDA) and so on. The touch panel may almost replace the mouse to be a computer input device.
Generally, after a user generates a touch point on the touch panel, the control circuit in the electronic device may calculate the position of the touch point immediately. After obtaining the position of the touch point, the electronic device may execute the corresponding programs.
There are multiple types of touch panels, and nowadays, a resistive touch panel is the most popular. The operating principle of the resistive touch panel is illustrated hereinbelow.
As shown in FIG. 1A, it is a side view showing a conventional resistive touch panel. Multiple strip-shaped indium tin oxide (ITO) layers 102 are formed on the surface of a transparent glass substrate 100. In addition, multiple strip-shaped ITO layers 112 are formed on the surface of a transparent film 110. The strip-shaped ITO layers 102 on the transparent glass substrate 100 are perpendicular to the strip-shaped ITO layers 112 on the transparent film 110. In addition, multiple transparent spacer dots 120 isolate the strip-shaped ITO layers 102 on the transparent glass substrate 100 and the strip-shaped ITO layers 112 on the transparent film 110 to prevent them from contacting.
When the user presses the transparent film 110 with a finger or a stylus, the strip-shaped ITO layer 112 on the transparent file 110 is transformed and contacts the strip-shaped ITO layer 102 on the transparent glass substrate 100. The control circuit (not shown) of the touch panel calculates the position of the touch point.
As shown in FIG. 1B, it is a top view showing the conventional resistive touch panel. For example, four electrodes are disposed around the touch panel 10. They are a negative Y (Y−) electrode, a positive Y (Y+) electrode, a negative X (X−) electrode and a positive X (X+) electrode. In addition, the strip-shaped ITO layers 102 on the glass substrate are arranged vertically, and the two ends of all the strip-shaped ITO layers are connected to the negative Y (Y−) electrode and the positive Y (Y+) electrode. The strip-shaped ITO layers 112 on the transparent film 110 are arranged horizontally, and the two ends of all the strip-shaped ITO layers 112 are connected to the negative X (X−) electrode and the positive X (X+) electrode. All the strip-shaped ITO layers 102 and 112 may be equivalent to resistors.
In addition, the control circuit 150 is respectively connected to the negative Y (Y−) electrode, the positive Y (Y+) electrode, the negative X (X−) electrode and the positive X (X+) electrode via the Y− line, the Y+ line, the X− line and the X+ line. When touch points are generated on the touch panel 10, the control circuit 150 may obtain the position of the touch point quickly.
As shown in FIG. 2A, it is a schematic diagram showing that whether touch points are generated on the conventional resistive touch panel is detected. First, to get whether the user generates a touch action on the touch panel, the control circuit (not shown) connects a power source (Vcc) to the positive X (X+) electrode, connects the ground end to the negative Y (Y−) electrode, connects the negative X (X−) electrode to the control circuit to provide voltage Va and open the positive Y (Y+) electrode.
Obviously, when the user does not press the touch panel, the upper strip-shaped ITO layers and the lower strip-shaped ITO layers do not contact each other. Therefore, the control circuit may receive the voltage Va at the negative X (X−) electrode which is equal to the voltage Vcc. It represents that the user does not press the touch panel.
When the user presses the touch panel with a stylus 140 or a finger, the upper strip-shaped ITO layers contact the lower strip-shaped ITO layers at the touch point A. Therefore, the control circuit detects that the negative X(X−) electrode receives a voltage
  (      Va    =                            (                                    R              ⁢                                                          ⁢              4                        +            Rz                    )                ·        Vcc                              R          ⁢                                          ⁢          1                +        Rz        +                  R          ⁢                                          ⁢          4                      )which is smaller than the voltage Vcc. That is, it is determined that the user presses the touch panel. The contact resistance Rz is the contact resistance when the two strip-shaped ITO layers contact each other.
As shown in FIG. 2B, it is a schematic diagram showing the process of calculating the horizontal position of the touch point on the conventional resistive touch panel. The control circuit calculates the position of the touch point after it is determined that the user generates a touch action. To obtain the horizontal position of the touch point, when the control circuit detects the touch action, it performs a switching process to connect a power source (Vcc) to the positive X (X+) electrode, connects the ground end to the negative X (X−) electrode, connects the positive Y (Y+) electrode to the control circuit to receive the voltage Vx and open the negative Y (Y−) electrode.
Obviously, the voltage on the positive Y (Y+) electrode is
  Vx  =                    R        ⁢                                  ⁢                  2          ·          Vcc                                      R          ⁢                                          ⁢          1                +                  R          ⁢                                          ⁢          2                      .  As shown in FIG. 2B, when the touch point A gets closer to the right side, the voltage Vx is higher, and on the contrary, when the touch point A gets closer to the left side, the voltage Vx is lower. Therefore, the control circuit may convert the voltage Vx via an analog to digital conversion to obtain the horizontal position of the touch point.
As shown in FIG. 2C, it is a schematic diagram showing the process of calculating the touch point on the conventional resistive touch panel. To obtain the vertical position of the touch point A, when the control circuit calculates the horizontal position of the touch point A, it performs the switching process again to connect a power source (Vcc) to the positive Y (Y+) electrode, connect the ground end to the negative Y (Y−) electrode, connect the positive X (X+) electrode to the control circuit to receive the voltage Vy and open the negative X (X−) electrode.
Obviously, the voltage at the positive X (X+) electrode is
  Vy  =                    R        ⁢                                  ⁢                  4          ·          Vcc                                      R          ⁢                                          ⁢          3                +                  R          ⁢                                          ⁢          4                      .  As shown in FIG. 2C, when the touch point A gets closer to the upper side, the voltage Vy is higher, and on the contrary, when the touch point A gets closer to the lower side, the voltage Vy is lower. Therefore, the control circuit may convert the voltage Vy via an analog to digital conversion to obtain the vertical position of the touch point.
Obviously, the touch panel is a detecting area surrounded by four electrodes (the negative Y electrode, the positive Y electrode, the negative X electrode and the positive X electrode). In addition, FIG. 2A shows the detection of whether the touch action is generated on the detecting area. When the touch action is generated, the control circuit performs the steps in FIG. 2B and FIG. 2C to obtain the horizontal position and vertical position of the touch point. On the contrary, when the touch action is not generated, the control circuit stays in the state of FIG. 2A and continues waiting for the generation of the touch action.
Since the conventional resistive touch panel is an analog touch panel, when multiple touch points are generated by a user in the touch panel simultaneously, the control circuit is unable to detect multiple touch points, and it may calculate a wrong touch point. For example, as shown in FIG. 3, it is a schematic diagram showing that multiple touch points are generated on the conventional resistive touch panel. The detecting area 160 is defined by four electrodes (not shown). When two touch points A1 and A2 are generated simultaneously in the detecting area 160, supposing that the horizontal position and vertical position of the touch point A1 is (x1, y1), and the horizontal position and vertical position of the touch point A2 is (x2, y2), the control circuit may wrongly detect a third touch point A3. The horizontal position and vertical position of A3 may be detected to be (x1+x2)/2 and (y1+y2)/2.
To detect multiple touch points on the resistive touch panel, the new type of resistive touch panel is developed. As shown in FIG. 4A, it is a schematic diagram showing the resistive touch panel which may detect multiple touch points. In FIG. 4A, the resistive touch panel includes four groups of electrodes (X1+ to X3+, X1 to X3−, Y1+ to Y4+, and Y1− to Y4−). In addition, in the resistive touch panel, the X+ group and X− group have three electrodes, respectively, and the Y+ group and Y− group have four electrodes, respectively. The amount of electrodes in each group is not limited herein, and it may be changed.
In FIG. 4A, three electrodes in a positive X (X+) group are a positive X1 (X1+) electrode, a positive X2 (X2+) electrode and a positive X3 (X3+) electrode; three electrodes in a negative X (X−) group are a negative X1 (X1−) electrode, a negative X2 (X2−) electrode and a negative X3 (X3−) electrode; three electrodes in a positive Y (Y+) group are a positive Y1 (Y1+) electrode, a positive Y2 (Y2+) electrode, a positive Y3 (Y3+) electrode and a positive Y4 (Y4+) electrode; and three electrodes in a negative Y (Y−) group are a negative Y1 (Y1−) electrode, a negative Y2 (Y2−) electrode, a negative Y3 (Y3−) electrode and a negative Y4 (Y4−) electrode. Obviously, four groups of electrodes divide the resistive touch panel into twelve areas. For example, the X1+ electrode, the X1− electrode, the Y1+ electrode and the Y1− electrode form the detecting area D11, and others are by parity of reasoning.
In addition, the multiplex switching circuit 230 are connected to all electrodes, and it may selectively connect an X+ line to part or all electrodes in the X+ group, connect an X− line to part or all electrodes in the X− group, connect a Y+ line to part or all electrodes in the Y+ group and connect a Y− line to part or all electrodes in the Y− group according to a control signal of the control circuit 250.
The touch panel which may detect multiple touch points in the embodiment of the invention is illustrated hereinbelow in detail. As shown in FIG. 4B, it is a schematic diagram showing an equivalent circuit during the touch point detecting procedure. To detect whether a touch action is generated on the touch panel 200, the control circuit 250 connects the X+ line to all electrodes in the X+ group, connects the X− line to all electrodes in the X− group, connects the Y+ line to all electrodes in the Y+ group and connects the Y− line to all electrodes in the Y− group. In addition, the control circuit 250 performs the first switching action to connect a power source (Vcc) to the X+ line, connect the ground end to the Y− line, take a signal of the X− line as a determining signal, and open the Y+ line. The control circuit 250 may detect whether a touch action is generated in all areas of the touch panel 200, and the detecting way is the same as that in FIG. 2A, and it is not illustrated herein for a concise purpose.
For example, when the control circuit 250 obtains that the user generates a touch point (such as the touch point B1), the control signal of the control circuit 250 controls the multiplex switching circuit 230 to orderly connect the X− line, the X+ line the Y− line and the Y+ line to the twelve detecting areas and detects whether the touch point is generated in the twelve detecting areas. At last, as shown in FIG. 4C, the touch point B1 is obtained at the area D31 defined by the Y1+, Y1−, X3+ and X3− electrodes, and the horizontal position and vertical position of the touch point B1 is obtained. In addition, the way of calculating the position of the touch point B1 is the same as those in FIG. 2B and FIG. 2C, and it is not illustrated again.
Similarly, as shown in FIG. 5, when multiple touch points (such as B1, B2 and B3) are generated at a time by the user, the control circuit 250 obtains that the user generates the touch action. However, the control circuit 250 cannot obtain whether the user generates a single touch point or multiple touch points at the moment.
Then, the control signal of the control circuit 250 controls the multiplex switching circuit 230 to connect the X− line, the X+ line, the Y− line, and the Y+ line to the twelve detecting areas and detects whether the touch point is generated in the twelve detecting areas. At last, it is known that the detecting area D13, the detecting area D31, the detecting area D33 have a touch point, respectively, and the control circuit may calculate the position of the touch point B2 in the detecting area D13, the position of the touch point B1 in the detecting area D31 and the position of the touch point B3 in the detecting area D34.
Sometimes, the user may carelessly generate a plurality of touch points, and the control circuit of the conventional touch panel which may detect multiple touch points also calculates the positions of the touch points. As shown in FIG. 6, when the user operates the touch panel with the stylus 140, he or she always puts the finger 130 or the palm 135 on the touch panel 200. At that moment, the control circuit calculates multiple touch points. However, the touch point generated by the finger or the palm is not the effective touch point.